Initiating and controlling underground combustion



May 28, 1963 T. w. LEGATSKI 3,091,225

INITIATING AND CONTROLLING UNDERGROUND comsuswrcm 2 Shae Filed Dec. 29.1958 mm 2 20 m w 52 mom owximmm ENTOR. T. W. L EGATSK I W W? 9 TEE NM MA TTORNEKS May 28, 1963 T. w. LEGATSKI INITIATING AND CONTROLLINGUNDERGROUND COMBUSTION Filed Dec.

INVENTOR. TW. LEGATSKI ATTORNEYS United States Patent 3,091,225INITIATING AND CONTROLLING UNDER- GROUND COMBUSTION Theodore W.Legatslri, Bartlesville, Okla., assignor to Phillips Petroleum Company,a corporation of Delaware Filed Dec- 29, 1958, Ser. No. 783,447 7Claims. (Cl. fill-156) This invention relates to apparatus forinitiating and controlling combustion in a subterranean formationcontaining carbonaceous matter from a borehole penetrating theformation.

In situ combustion in the recovery of a diflicultly flowable hydrocarbonfrom underground strata containing such hydrocarbons or carbonaceousmaterial is becoming more prevalent in the petroleum industry. In thistechnique of production, combustion is initiated in the carbonaceousstratum and the resulting combustion zone is caused to move through thestratum by either inverse or direct air drive whereby the heat ofcombustion of a substantial proportion of the hydrocarbon in the stratumdrives out and usually upgrades a substantial proportion of theremaining hydrocarbon material. By the term remaining hydrocarbonmaterial is meant that hydrocarbon material recovered and which is notconsumed in the combustion.

The ignition of carbonaceous material in a stratum around a borehole,followed by injection of air through the ignition borehole and recoveryof product hydrocarbon in combustion gas through another borehole in thestratum, is a direct air drive process for clfecting in situ combustionand recovery of hydrocarbons from the stratum. In this type ofoperation, the stratum usually plugs in front of the combustion zonebecause a heavy viscous fluid bank collects in the stratum in advance ofthe combustion zone and prevents movement of air to the combustionprocess. To overcome this ditficulty and permit the continued progressof the combustion zone through the stratum, inverse air injection hasbeen resorted to. By this latter technique, a combustion zone isestablished around an ignition borehole by any suit able means and airis fed through the stratum to the combustion zone from one or more otherboreholes.

In operating with either direct or indirect air injection to producehydrocarbons from a carbonaceous stratum by in situ combustion, it isnecessary to ignite first the carbonaceous material in the stratumaround. a borehole. Various methods of igniting this carbonaceousmaterial have been devised. Also, many burners have been devised fordownhole use, such as gas fired burners and electric heaters. Onedifi'iculty in the use of any of these types of burners in such downholcoperation is that the formation tends to become overheated in theimmediate vicinity of the burner and the remaining portion of theborehole through the formation may not. be heated sufficiently toinitiate combustion. Thus, there is overheating at one point andunderheating at another point.

Accordingly, it is an object of this invention to provide a downholeheater of such construction that heat is uniformly transferred to theface of the borehole in the carbonaceous material containing formation.Another object of this invention is to provide a heater for heating theformation containing carbonaceous material which distributes heat ofsufficient intensity for ignition or the carbonaceous matter at alllevels of the formation face exposed in the borehole. A further objectof this invention is to provide a downhole heating apparatus which doesnot overheat at one level and underheat at another level. Other objectsand advantages of my invention will be realized by those skilled in theart upon consideration of the accompanying disclosure.

3,091,225 Patented May 28, 1963 In a copending application, Serial No.741,329, filed June 11, 1958, now Patent No. 3,035,638, is a full andcomplete description of a method for initiating and maintaining inversein situ combustion in a subterranean carbonaceous material containingformation. In this application. it is stated that one important point ofsaid onpcnding application in solving the problem of maintaining in situcombustion by inverse air flow is to mix a small percentage by volume ofa combustible gaseous material with air and inject this mixture into aninput well or borehole in such a manner that this mixture of fuel andair flows through the carbonaceous matter containing formation towardthe ignition well. The ignition well as considered herein is theborehole extending from the surface of the ground into the carbonaceousmaterial containing formation from which the formation is ignited in thecombustion operation. The injection well or borehole is the boreholeinto which the mixture of air or air and fuel gas is injected into theformation for maintaining this combustion. In said copendingapplication, a mixture of air and fuel gas suitable for maintainingcontinuous combustion within the carbonaceous material containingformation contained from about one to five percent by volume and moredesirably from about two to four percent of fuel gas by volume. Propanewas disclosed as being a preferred fuel gas but other fuel gases thanpropane, for example, ethane or even methane, that is either puremethane or in the form of natural gas is sometimes used. It is preferredthat the B.t.u. con tent of the fuel gas used in such an operation berelatively high and, for this reason, the use of propane is preferred.

In the drawing, FIGURE 1 is a longitudinal view, partly in section, of apreferred embodiment of my invention. FlGURE 2 is a longitudinal view,partly in section, of another embodiment of heating apparatus of myinvention. FIGURE 3 illustrates still another embodiment of heater of myinvention. FIGURE 4 is a longitudinal view, partly in section, of stillanother embodiment of my invention. FIGURE 5 illustrates, in digrammaticform, a sectional view through a carbonaceous material bearing formationand overlying strata illustrating a method of initiating combustionwithin a carbonaceous material bearing formation. FIGURE 6 illus tratesone method for recovering carbonaceous material from a carbonaceousmaterial containing zone being produced by underground combustion.

Referring to the drawing and specifically to FIGURE 1, this embodimentof formation heater involves a, tubular outer shell 12 in which isdisposed a tubular shell 13 of smaller diameter than shell 12. These twotubular shell members are disposed substantially concentrically withrespect to one another and at a spaced distance so as to provide anannulus 23 therebetween. The upper end of annulus 23 is closed by aclosure 27 as illustrated. The bottom ends of shells 12 and 13 areclosed as illustrated by substantially semispherical closures 14 and14a, respectively. Disposed within annulus 23 and the lower portionbetween closures 14 and 14a is an easily meltable and boilable metal 20.An upper closure member or cover 22 is disposed as illustrated forconfining combustion gases and directing same to a vent pipe 24.

Disposed within the inner shell 13 is a burner, that is, a fuel gasburner which comprises a burner tip 25 surrounded by a burner shield 15.Connected with burner tip 25 are pipes 16 and 17 through which air andfuel gas, respectively, are passed from the surface of the ground. Theburner is lit or in other words the fuel gas is ignited as by asparltplug 19 energized by an electric current passed through wires 18from above ground. As is well known in such art, a high voltage lowamperage current is required to operate such an ignitor.

A burner or heat transfer apparatus of this type operates in thefollowing manner. Fuel gas and air are passed downward through pipes 16and 17, respectively, and then electric current is passed through wires18 to form a spark at spark plug 19 which in turn ignites the gas. Whenthe gas has been ignited and flame issues from within burner shield 15,the apparatus then starts to become heated. The metal 20 in the bottomportion of this heater is such a metal as sodium, potassium, lithium,rubidium, caesium, or a mixture of any two or more of these metals. Ofthese metals, caesium boils at a temperature of 1238 F. and lithiumboils at a temperature of about 2437 F., these two temperaturesrepresenting the extreme limits of boiling points of these severalmetals. It is preferred to use metallic sodium in this apparatus becauseit is less expensive to purchase. Metalic sodium boils at a temperatureof 1615 F. Thus, upon ignition of the gas at burner 25, the shielddirects the flame downward against the lower portion of the inner shell13 and at closure member 14a so that the fiame will be directedsubstantially toward the metal 20. Upon continued heating, the metal isgradually raised to a temperature approaching its boiling point. Whenthe metal begins to boil, vapor rises upward in annulus 23 and heats thewalls of the inner and outer shells 12 and 13, respectively. The wall ofthe inner shell 13, is, of course, quite hot because it is exposed tothe temperature of the combustion gas. The wall of shell 12, beingadjacent the carbonaceous material bearing formation is materiallycooler than shell 13. As the vapor of the metal rises in annulus 23, itcondenses mainly on the surface of shell 12. As the metal shell becomesheated by condensation of the vapor, the vapor rises higher up theannulus until finally the entire inner surface 21 of shell 12 is incontact with condensing metal vapor and is thus heated to a sufficientlyhigh temperature. It is realized by those skilled in the art that such ameans of distributing heat all the way up and down the heater isparticularly adapted to heating uniformly an object to be heated. Thus,by the construction of this apparatus of such length that it extends inthe borehole across the entire face of the carbonaceous materialcontaining formation, the entire surface of the formation becomes heatedto a desired temperature. When this surface of the carbonaceous materialcontaining formation exposed to the borehole becomes sufficiently hotthen upon arrival of air from an adjacent air input well conditions areright for ignition to begin. As mentioned hereinbefore and as fullydisclosed in said copending application, by mixing a small percentage ofa combustible gas with the air being injected into an adjacent air inputwell upon ignition of the surface of the carbonaceous material bearingformation exposed to the heater a combustion front travels slowly andradially outwardly from the borehole into the formation.

On reference to FIGURE 5, reference numeral 11 identifies such a heattransfer assembly as illustrated in FIGURE 1 disposed in a borehole 63within a carbonaceous material containing subterranean formation 61.Pipes 16 and 17 pass air and fuel gas, respectively, to the burner ofthe heat transfer assembly and upon igniting spark plug 19 (FIGURE 1) bypassage of a high voltage current down leads 18 the burner within theheat transfer assembly 11 is lit and heating begins. After the heattransfer assembly 11 becomes well heated and heating is continued, thesurface of the well bore is raised to a combustion temperature and uponpassage of air or air and a fuel gas down a tube 70 in an air input well72 and through formation 61 combustion progresses from borehole 63 in adirection toward borehole 72. Reference numeral 62 identifies theleading surface of a combustion zone as propagated in the manner justdisclosed. Borehole 63 is in terms of this art frequently referred to asan ignition well. Such ignition wells are ordinarily provided withcasing, as for example, a casing 64, which is provided with a head orcasing cover 65 at the head of the well. In FIGURE 5 air for passage topipe 16 to the burner in the heat transfer assembly is illustrated asbeing provided from the atmosphere by a pump 69 which transfers the airthrough a pipe 88 to tubing or pipe 16. A fuel gas from a source, notshown, for firing the heater is provided through a pipe by a pump 67 andthrough a pipe 86 and a pipe 89 with valves in these pipes being open,to tubing or pipe 17 for passage down the well to the burner.

The heater is operated in this manner until such time that it is certainthat the combustion in the formation had been well started and isprogressing satisfactorily. Progression of the combustion zone may beobserved by providing a small diameter well bore 74 which may be casedby a casing 75, as desired, and which is provided with one or morethermocouples 76. These thermocouples communicate to electricalapparatus above ground through a cable 77 to conventional electricalapparatus for converting electrical impulse to degrees F., for example.Such electrical equipment is well known in the art. At such a time thatthermocouples 76 indicate that the combustion zone has progressed asubstantial distance from the heat input well then the valves in pipes86 and 89 and in pipe 88 may be closed to shut off the flow of gas andair to the burner in the heat transfer assembly. When these valves areclosed and the flame in the heat transfer assembly is extinguished, theheat transfer assembly is pulled from the well by unbolting casing cover65 and pulling the tubes or pipes and the heater in a conventionalmanner.

While the heat transfer apparatus is being withdrawn from well bore 63,air with a small content of fuel gas is passed through tubing 70 intothe air input well 72 for maintenance of combustion within theformation. In this passage of the air and gas mixture down tubing 70,the gas is passed under the influence of pump 67 through pipe 85 andpipe 68 with the valve in that pipe being open and air from pump 69 ispassed through pipe 87 with the valve in this pipe being open and themixture then enters the air inlet pipe 70 for passage down the well.

After the heat transfer assembly 11 has been withdrawn from the ignitionwell 63, a production tubing is run into the well and is attached to thecasing by means of a casing cover similar to casing cover 65. In FIG-URE 6 is illustrated the well 63 provided with such a production tubing66 attached to the well casing by a casing cover 65a. After this tubing66 is run into the well and attached to the casing by the cover 65a,combustion gases and vaporous hydrocarbon material which leave theformation and enter well 63 at the borehole surface 73 enter tubing 66and are conducted up the well. This produced material leaves the wellhead, passes through a pipe 78 into a separator 79 in which producedliquids separate from produced gas. If desired, all or a portion of theproduced hydrocarbon material from production tubing 66 is by-passedfrom pipe 78 and passed through a by-pass line containing a condenserfor condensation of condensable material. This condenser can be a largesurface atmospheric condenser, or a liquid condenser in which thecoolant is a cooling water or the condenser may even be a refrigeratedcondenser. Whatever type of condenser is used, condensed and uncondensedmaterials pass on into separtor tank 79 in which gases are separatedfrom liquid. Liquid is passed from separator 79 through a pipe 80 into astorage tank 81 for such disposal as desired. Gases sepa rated inseparator 79 are withdrawn through a pipe 82 and, if desired, a smallportion of this produced gas is passed through a pipe 84 into pipe 86 ofFIGURE 5 and further passed through pipe 68 for use in producing theair-fuel gas mixture for injection into the air input well. Gasseparated in separator 79 and passed through pipe 82 not required forsuch combustion maintenance is withdrawn from the system through a pipe83 for such disposal as desired.

In FIGURE 2. is illustrated another embodiment of heater apparatusinvolving the principles of my invention. A difference between thisheater and the one illustrated in FIGURE 1 is in the actual fuel gasburner arrangement. The burner illustrated in FIGURE 2 is intended toutilize a premix air and fuel mixture in place of separate fuel gas andair. A premixed mixture of fuel gas and air is passed from the surfaceof the ground down the heat input well or ignition well through a pipe33 to the heating apparatus. Since the premixed air and fuel isobviously an explosive mixture, a flame arrestor 34 is provided in pipe33 at a point adjacent the heating apparatus. After passing through theflame arrestor 34 the mixture enters the actual heating apparatus andflame then passes through a flame tube 36 provided with openings 32 onlyat and near the lower end of the flame tube 36. Flame is needed only inthe general vicinity of the liquid metal 20 in the bottom portion of theheater. Heat issuing through the openings 32 in this lower portion offlame tube 36 heats the metal to a boiling temperature and upon boilingthe vapor rises up the annulus 23 and condenses mainly on the walls ofthe outer shell 12 for imparting heat to the formation to be ignited.The combustible mixture of gas and air is ignited by spark plug 19energized by high voltage current through leads 18 as mentionedhereinbefore. The vent pipe 24 is provided for passage of burned gasesup the well bore to the surface of the ground for disposal.

In FIGURE 3 is illustrated an embodiment of heater of my invention whichis heated by electrical means in place of a fuel gas. The main heatingportion of the apparatus that is the inner and outer shells 13 and 12,respectively, forming an annulus in the bottom of which is a quantity ofboilable metal, is all similar to that illustrated in FIGURES 1 and 2.For heating the metal in this embodiment, a heating coil 40 is woundaround the inner wall of the inner shell 13 and is held in place by arefractory cementing material 41, such as Kaocast, high alumina,castable, hydraulically setting refractory. The electrical heatingelement may be maintained or held in close contact with the inner wallof shell 13 in any other suitable manner, if desired. Lead wires 42conduct electric current from the surface of the ground down the wellbore to the resistance element 40. As the metal 20 is heated to itsboiling point vapor than passes upward in the annulus 23 to heat theWalls of the outer shell 12 for bringing to combustion temperaturecarbonaceous matter on the borehole walls of the formation. A cover 91is provided at the top of this apparatus to provide support for wires42. Cover 91 is provided with a vent 90 for inlet and outlet of gases ofexpansion formed during heating and cooling of this apparatus.

In FIGURE 4 is still another embodiment of my invention. In thisembodiment, heat is again supplied by combustion of a fuel gas with air.However, in place of having to provide one or more tubes or pipes forpassage of premixed air and fuel or air and fuel separately from thesurface of the ground down to the heating apparatus I provide bottles offuel gas and air under pressure with the apparatus. As illustrated inthis figure a case 45 is attached to the lower portion of the outershell 12. Case 45 houses a burner ring 52 which is connected by tubes 56and 57, respectively, to a fuel gas bottle 47 and to an air bottle 46.Tube 56 is provided with a solenoid valve 51 while tube 57 is providedwith a solenoid valve 50. These solenoid valves are operated from thesurface of the ground by passage of electrical impulse throughelectrical cable 54. Additional wires are provided in cable 54 fortransmission of high voltage current to a spark plug 53. In theaboveground operation, apparatus is so provided that upon closing of acircuit to solenoid valve 59 and 51 high voltage current issimultaneously passed to spark plug 53 so that upon passage of air andfuel gas through tubes 57 and 56, respectively, to burner ring 52 thespark plug becomes activated and ignites the fuel gas. Upon ignition ofthe gas the metal 20 becomes heated and finally boils. The operationfrom this point on is similar to that described relative to the heatingapparatus of FIGURES l, 2 and 3. The construction of the heaterapparatus is slightly different in this modification of FIGURE 4 than inthe other modification. This difference is that an opening 58 isprovided in the bottom of the heating apparatus for accommodation of theelectrical wiring. If the electrical wiring cable 54 were on the outsideof the heat transfer assembly 11 upon lowering this apparatus down theWell bore the cable might easily be injured so that the electricalportion of this apparatus would not function properly. After ignition ofgas in burner ring 52, it is immaterial whether the wiring at this pointis destroyed or not because it has fulfilled its purpose. Furthermore,burned gases from the flame issuing from burner 52 pass upward throughopening 58 and impart additional heat to the inner wall of the innershell 13 and these burned gases finally exit up the well through ventpipe 55 for such disposal as desired.

Materials of construction for use in building the heating apparatus ofmy invention may be selected from among those commerically availabletaking into consideration the particular metal 20 heated to boilingwithin the apparatus and further taking into consideration temperaturesinvolved. Some stainless steels withstand temperatures in the vicinityof 2600 to 2700" F. Such materials might be expected to withstandtemperatures within the ignition wells maintained for the length of timerequired to start combusion in the formation.

Referring again to FIGURE 4 the air containing bottle 46 is fixed tocase 45 by support 48 while the fuel gas bottle 47 is attached by member49 to case 45.

In FIGURE 2, cover 35 is provided for confining combustion gases fromburner tube 36 so as to direct them up the vent pipe 24.

In each case or type of heater described herein it is necessary andimportant that the length of the actual heat transfer portion of theapparatus be at least equal to the length of the borehole in thecarbonaceous material hearing formation. In other words, the length ofthe heater should be at least equal to the thickness of the carbonaceousmaterial containing formation for uniform heating to combustiontemperatures of the material in the formation. By so providing thisheater and with its unusually uniform distribution of heat throughoutits length hot spots and spots heated to too low a temperature are notinvolved. As is well known, portions of formations which are overheatedfrequently become sintered and more or less imprevious to the passage offluid. Furthermore, spalling and caving due to excessive temperatures orpartial fusing are not involved.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

I claim:

1. Apparatus for heating a subterranean formation containingcarbonaceous matter from a bore hole penetrating said formationcomprising, in combination, a first tubular member having the lower endthereof closed, a second tubular member having the lower end thereofclosed disposed within and along the axis of said first tubular member,said second member being disposed at a spaced distance from said firstmember thereby providing an annulus therebetween having completelyclosed ends, a body of metal having a boiling point between about l200and 2450 F. disposed in and partially filling said annulus at a lowerend thereof, said body of metal being present in an amount suificientupon boiling to substantially vaporize and fill said annulus withcondensing metal vapor, a closure member closing the end of said secondtubular member at an upper end of said annulus, means supported by saidclosure member for heating said metal which is so adapted as to providea combustion area in a position adjacent to the lower end of saidannulus and said body of metal so as to effect vaporization of same, anda vent in said closure member and in communication with said combustionarea.

2. The apparatus of claim 1 wherein said metal is selected from thegroup consisting of sodium, potassium, lithium, rubidium, cesium, andmixtures of two and more of these metals.

3. The apparatus of claim 1 wherein said means for heating said metal isa gas fueled burner.

4. The apparatus of claim 3 wherein said gas fueled burner for heatingsaid metal is disposed within the inner of said first and second tubularmembers, and said burner being so positioned as to direct flamedownward.

5. The apparatus of claim 3 wherein said axis is vertically disposed andsaid closure member is at about the top of the apparatus and whereinsaid gas fueled burner is disposed outside the outer tubular member ofthe first and second tubular members and below the lower closure meansof said separate closure means, a separate vent in said lower closuremeans and in said closure member, first and second bottles for fuel gasand a combustion supporting gas, respectively, supported by and belowsaid burner, separate conduit means communicating said first and secondbottles with said burner, separate valves in each conduit means foropening said valves and means for igniting fuel gas in said burner.

6. Apparatus for heating a subterranean formation containingcarbonaceous matter from a bore hole penetrating said formationcomprising, in combination, a first tubular member, a second tubularmember disposed within and along the axis of said first tubular member,said second member being disposed at a spaced distance from said firstmember thereby providing a completely closed annulus thcrebetween, abody of metal having a boiling point between about 1200 and 2450 F.disposed in and partially filling said annulus at one end thereof, saidbody of metal being present in an amount sufiicient upon boiling tosubstantially vaporize and fill said annulus with condensing metalvapor, and means for heating said metal by an upper portion of saidtubular member so as to effect vaporization of said body of metal, saidmeans for heating being external said annulus and adjacent said body ofmetal in same.

7. In the apparatus of claim 6, wherein said means for heating saidmetal is a gas fueled burner disposed within said second tubular member,a conduit communicating with said burner and extending through saidclosure member for passage of premixed fuel gas and gaseous oxygen tosaid burner, a flame arrestor in said conduit, and means to ignite fuelgas in said burner.

References Cited in the file of this patent UNITED STATES PATENTS1,146,310 Colby July 13, 1915 1,639,114 Smith Aug. 16, 1927 1,840,588Knox Jan. 12, 1932 1,983,386 Mikeska Dec. 4, 1934 2,163,599 Houdry June27, 1939 2,556,984 Smith June 12, 1951 2,584,606 Merriam et al. Feb. 5,1952 2,669,661 Riddiford et a1. Feb. 16, 1954 2,717,580 Maher et al.Sept. 13, 1955 2,820,134 Kobayaski Jan. 14, 1958 2,865,827 Dwyer Dec.23, 1958 2,893,701 Bell July 7, 1959 2,902,270 Salomonsson et a1 Sept.1, 1959 2,932,352 Stegemeier Apr. 12, 1960 FOREIGN PATENTS 808,316France Nov. 14, 1936 902,703 France Dec. 22, 1944

1. APPARATUS FOR HEATING A SUBTERRANEAN FORMATION CONTAININGCARBONACEOUS MATTER FROM A BORE HOLE PENETRATING SAID FORMATIONCOMPRISING, IN COMBINATION, A FIRST TUBULAR MEMBER HAVING THE LOWER ENDTHEREOF CLOSED, A SECOND TUBULAR MEMBER HAVING THE LOWER END THEREOFCLOSED DISPOSED WITHIN AND ALONG THE AXIS OF SAID FIRST TUBULAR MEMBER,SAID SECOND MEMBER BEING DISPOSED AT A SPACED DISTANCE FROM SAID FIRSTMEMBER THEREBY PROVIDING AN ANNULUS THEREBETWEEN HAVING COMPLETELYCLOSED ENDS, A BODY OF METAL HAVING A BOILING POINT BETWEEN ABOUT 1200*AND 2450*F. DISPOSED IN AND PARTIALLY FILLING SAID ANNULUS AT A LOWEREND THEREOF, SAID BODY OF METAL BEING PRESENT IN AN AMOUNT SUFFICIENTUPON BOILING TO SUBSTAN-